With a wheel loader, taken as an example as one type of working vehicle, an output of the engine is used as power for working and also as power for traveling. With the wheel loader, a load such as earth or sand or the like is scooped up by a bucket as a working apparatus, the bucket is lifted up by a boom, and then the load is dumped upon a bed or the like of a truck. It is possible to enhance working efficiency by raising the bucket which the load has been filled rapidly.
Thus, in the prior art, during loading operation, an operator operates a brake pedal and an accelerator pedal at the same time. Due to this, it has been proposed to increase a rotational speed of a hydraulic fluid pump during low speed traveling, so as to increase the amount of hydraulic fluid supplied to the working apparatus (refer to Patent Document #1). It should be understood that a technique is also per se known for controlling the degree of engagement of a clutch according to the difference between rotational speeds of left and right drive wheels.    Patent Document #1: JP-A-2006-521238.    Patent Document #2: JP-A-2001-146928.